Is there a way of searching for a list of users on AD who have not logged on in the last year?

Question

I am trying to find a way of getting a list of UserPrincipal objects that have not logged in for a year. There is a Last Logon property on the object, but I can't figure out how to do a less than style of query, everything I have seen are only equal to and I can't find anything that uses the property in the search.

Am I barking up the wrong tree with this not being possible?

This is the code I have so far, the "issue" I have is that I am having to develop this blind and I am not able to run it until it goes to the customers system. At the moment it is just throwing a generic error complaining that something is null, but no reference to what object or line. Which to me is barmy as it is in a try with a catch.

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim domain As PrincipalContext = New PrincipalContext(ContextType.Domain, "DomainNameHere")
        Dim up As New UserPrincipal(domain)
        Dim search As New PrincipalSearcher()
        Dim results As PrincipalSearchResult(Of UserPrincipal)
        Dim listResults As New List(Of UserPrincipal)
        'Dim usr As UserPrincipal = UserPrincipal.FindByIdentity(domain, HttpContext.Current.User.Identity.Name)

        Try

            dt = New DataTable
            dt.Columns.Add(New DataColumn("PUID", GetType(String)))
            dt.Columns.Add(New DataColumn("Name", GetType(String)))
            dt.Columns.Add(New DataColumn("Role", GetType(String)))
            dt.Columns.Add(New DataColumn("LastLogon", GetType(String)))
            dt.Columns.Add(New DataColumn("GroupCount", GetType(String)))

            'dt.Rows.Add(usr.SamAccountName, usr.GivenName & " " & usr.Surname, usr.DisplayName, usr.LastLogon.ToString)

            search.QueryFilter = up
            results = (From principal In search.FindAll() Select TryCast(principal, UserPrincipal))
            listResults = results.Where(Function(u) u.LastLogon < Today.AddYears(-1)).OrderBy(Function(u) u.LastLogon).ToList

            'results = UserPrincipal.FindByLogonTime(domain, Now.AddYears(-1), MatchType.LessThanOrEquals)
            'results.OrderBy(Function(u) u.LastLogon)

            For Each u As UserPrincipal In listResults
                If Not IsNothing(u) Then
                    Dim puid As String = "-"
                    Dim name As String = "-"
                    Dim role As String = "-"
                    Dim logon As String = "-"
                    Dim groupCount As String = "0"

                    If Not IsNothing(u.SamAccountName) Then puid = u.SamAccountName
                    If Not IsNothing(u.GivenName) AndAlso Not IsNothing(u.Surname) Then puid = u.GivenName & " " & u.Surname
                    If Not IsNothing(u.DisplayName) Then role = u.DisplayName
                    'If Not IsNothing(u.DisplayName) AndAlso u.DisplayName.IndexOf("(") > 5 Then role = Left(Right(u.DisplayName, u.DisplayName.Length - u.DisplayName.IndexOf("(") - 1), Right(u.DisplayName, u.DisplayName.Length - u.DisplayName.IndexOf("(") - 1).Length - 1)
                    If Not IsNothing(u.LastLogon) AndAlso IsDate(u.LastLogon) Then logon = CDate(u.LastLogon.ToString).ToString("dd MMM yyyy")

                    'Dim groups As PrincipalSearchResult(Of Principal) = u.GetGroups
                    'Dim listGroups As New List(Of String)
                    'Dim i As Integer = 0

                    'For Each grp As Principal In groups
                    '    If grp.ToString.ToUpper.Contains("NAVY") Then i += 1
                    'Next

                    'groupCount = groups.Count.ToString & " (" & i.ToString & ")"

                    dt.Rows.Add(puid, name, role, logon, groupCount)
                End If
            Next

            rUsers.DataSource = dt
            rUsers.DataBind()
        Catch ex As Exception
            litError.Text = "Domain: " & domain.ToString & "<br />"
            litError.Text += "User Principal: " & up.ToString & "<br /><br />"
            litError.Text += "Source: " & ex.Source.ToString & "<br /><br />Message: " & ex.Message.ToString & "<br /><br />Inner Exception:<br />" & ex.InnerException.ToString & "<br /><br />Stack Trace:<br />" & ex.StackTrace
        End Try

    End Sub